The invention relates to a connector having a film located in an interior region. More particularly, the invention relates to a connector wherein an index matching film is positioned between the end faces of two optical fibers optically coupling the two fibers together.
In recent years, electro-optical equipment has begun to replace electronic equipment for certain applications, for example, for telecommunications networks. This trend is expected to continue because of the inherent advantages that electro-optical equipment has over electronic equipment for these kinds of applications. In order to interconnect various pieces of electro-optical equipment, fiber optic cables are used. The fiber optic cables comprise optical fibers surrounded by strength members and external jacketing with connectors at the ends thereof. The appearance of the fiber optic cables resembles electric shielded cables, such as coaxial cables, but they are smaller in size and lighter in weight. A great deal of effort has been expended in developing connectors for interconnecting fiber optic cables with low loss and low reflection (high return loss).
The prior art teaches various procedures for obtaining low loss and high return loss connections between lengths of optical fibers. One way of doing this is simply to press the ends of the fibers together by means of a connector, for which various designs are known in the art. Thus, the optical fibers are optically coupled together when the ends of the fibers are brought into physical contact with each other. The ends of the fibers should first be prepared by polishing to obtain a more uniform defect-free surface that results in lower signal loss.
Ferrule-type connectors are often used to bring the ends of two optical fibers into physical contact for the purpose of optically coupling them together. For this kind of connector to work successfully, it is required that the optical fibers be flush with or slightly protruding above the mating end faces of the ferrules. Very close tolerances are required to maintain optical contact. Substantial deviations from these conditions tend to result in loss of optical contact and high reflection (or low return loss). Furthermore, any foreign matter, such as dirt, which may be introduced into the gap between the two mating end faces will prevent the optical fibers from being in optical contact with each other.
Heretofore, in order to maintain optical contact, refractive index matching oils or gels have been used to fill the gap between the end faces of the optical fiber containing ferrules. However, such fluids or gels themselves tend to trap foreign matter, particularly when the fibers are unmated for a period of time and then remated, which again may increase losses. Furthermore, such fluids and gels are not very suitable when multiple mate/unmate operations are required.
U.S. Pat. No. 4,221,461 discloses the use of transparent thermoplastic polyurethane materials for coating the ends of optical fibers to reduce coupling losses between lengths of fiber. The coating adheres to the ends of the fibers and is compliant so as to deform elastically when pressed upon making connection with the end of another optical fiber. The coatings are cast onto the ends of the fiber by dissolving the polyurethane materials in a solvent, applying the solution to the fiber ends, and heating to remove the solvent. One of the disadvantages of this procedure is that the coating must be applied to the end faces of fiber under clean conditions to avoid trapping dirt.
U.S. Pat. No. 4,634,214 discloses a ferrule-type connector assembly for optically coupling two lengths of optical fiber. The connector assembly includes a connector plug attached to the end of a fiber optic cable and a connector receptacle which receives two such connector plugs. Each connector plug has a ferrule with a bore through which the optical fiber passes. A pedestal made from an index matching compliant material is located on the end face of the ferrule.
In the system of U.S. Pat. No. 4,634,214 the index matching material in the form of a pedestal is attached to the end face of the ferrule. This system has several disadvantages. The pedestal does not adhere to the ferrule too well. The pedestal has a tendency to become detached from the ferrule. Furthermore, a pedestal must be mounted in a cumbersome procedure on the end of each optical fiber cable which may be inserted into the connector receptacle.
Clearly, it would be much more desirable to have a system wherein an index matching material forms part of the connector receptacle, i.e., wherein an index matching material is located and remains inside a connector receptacle rather than being attached to and travelling with the connector plug at the end of an optical fiber cable.